The invention relates to gas turbines and, more particularly, to a method of effectively removing residual liquid fuel to reduce fuel coking.
When a gas turbine is shut down or transferred to gas-fuel operation after running on liquid fuel, a significant amount of liquid fuel may be left in or on the passages, crevices and walls of the liquid fuel system components, including the mixing valves and combustion nozzles. It is important for the residual liquid fuel to be sufficiently removed from inside the mixing valve assembly and combustion nozzles so that fuel coking and subsequent component malfunction does not occur. That is, when exposed to the high temperatures around the gas turbine, residual liquid fuel in those components tends to cook down into a thick sludge or varnish or “coke.” That layer of coked fuel can inhibit valve operation and clog combustion passages, greatly reducing system reliability and operability.
It would be desirable to provide a methodology by which the liquid fuel is more completely removed from the valves and nozzles so that fuel no longer remains present in locations where it may be susceptible to coking. Prevention of coke formation is important to the reliability and operability of the liquid fuel system.